There is always an awkward start-up phase with the CPM model, where you don't have enough impressions to join a premium network / aggregator. But as others have said, once you are able to generate visitors that view multiple pages per visit and have consistent levels of traffic from tier 1 countries, your CPM goes up considerably.
Also, it's always wise to have other revenue streams to complement your traffic arbitrage efforts. If you have a niche website, build up an email list and send through offers regularly (in between value posts). Once you have a steady stream of traffic, you'll also likely attract some paid posts and direct paid ad placements.
